This invention relates to an apparatus for inducing vibrations in an airfoil, particularly an airfoil used in various components of a gas turbine engine.
Fan or compressor airfoil design is an area of gas turbine engine technology presently in need of advancement. In order to achieve improvements in engine and aircraft efficiency, new compact lightweight and aerodynamically optimized airfoils must be developed. A limiting constraint which must be given thorough consideration in the design of new airfoils is the dynamic aeroelastic interaction between the airfoil and the gas flow field in which it operates. While analytical investigations may be undertaken to mathematically model the aforedescribed aeroelastic interaction phenomenon, such models cannot be accepted as accurate and correct until verified through empirical data.
In the past such models have been partially verified by the acquisition of empirical data from experimental testing involving the excitation or oscillation of the airfoil in a torsional mode; that is, a rotational mode about the longitudinal axis of the airfoil. Some test apparatus, which has been used to generate the data, can be generally characterized as an electromagnetic system which rotatively oscillates the airfoil about its longitudinal axis at appropriate amplitudes and frequencies to attempt to simulate the vibration caused by the aeroelastic interaction between the airfoil and gas flow field.
Past analytical investigations have met with only partial success in mathematically modeling the aforedescribed aeroelastic interaction since they have failed to recognize that a typical airfoil will vibrate in a gas flow field not only in a torsional mode but also in flexural mode; that is in a direction perpendicualr to the airfoil surfaces. Said another way, the aeroelastic vibration of a typical airfoil disposed in a gas stream will exhibit both a torsional mode and a flexural mode each of which must be taken into consideration when mathematically modeling the interaction. This present invention is directed at apparatus for oscillating the airfoil simultaneously in a flexural mode and a torsional mode to simulate the vibration caused by the aeroelastic interaction between the airfoil and the gas flow field in which it is disposed.